Contact dermatitis

Chapter 6 Contact dermatitis

Introduction

Contact dermatitis (CD) refers to adverse cutaneous reactions resulting from direct contact with an external agent. It is a common inflammatory skin condition that primarily affects older children and adults. CD can be allergic (ACD) or irritant (irritant CD). In some cases of ACD, exposure to sunlight is required for sensitization (photoallergic CD). CD is often due to a chemicals encountered at work (occupational CD), which may have serious financial implications.

Common sensitizing agents for ACD include nickel, plants (e.g. poison ivy), and occupational sensitizers (e.g. epoxy resins) (Table 6.1). Latex can cause immediate (IgE- mediated) reactions, as well as ACD. A concurrent allergic or irritant CD may also develop from non-latex chemicals used in rubber. In irritant CD, skin irritants produce eczematous skin changes. In photoallergic CD, exposure to sun light (i.e. ultraviolet light) is essential for the initiation of an allergic response to the offending agent. Thus, it affects exposed areas, such as the face and arms. Workrelated skin diseases account for approximately 50% of occupational illnesses (6.1, 6.2). Industries in which workers are at highest risk include manufacturing, food production, construction, printing, metal plating, leather work, and cosmetics.

Table 6.1 Common causes of ACD

Groups Examples Metals

Nickel sulphate, cobalt chloride Cosmetics

Balsam of Peru, fragrance mix Rubber products

Latex, thiuram mix, mercaptobenzothiazole, mercapto mix, black rubber mix, carba mix

Preservatives Thimerosal, formaldehyde, quaternium-15, potassium dichromate, paraben mix, ethylenediamine dihydrochloride

Glues, plastic Epoxy resin, para-tertiary-butylphenol formaldehyde resin, colophony Dyes Para-phenylenediamine Antibiotics Neomycin sulphate Vehicle (creams,

Wool alcohol lotions)

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6.1, 6.2 This patient worked in a supermarket staff canteen. She had irritant CD of face and hands to the disinfectant spray she was using to clean the surfaces. Dryness and scaling on a background of erythema are main features of chronic irritant CD. The patch test was negative, but symptoms improved when the use of the disinfectant spray was stopped.

Pathophysiology

ACD results from an antigen-specific, lymphocyte-mediated hyper-sensitivity reaction. The effector cells are CD8 T-cells, whereas CD4 T-cells function as regulatory cells. Most antigens causing ACD are small molecules that may act as hapten, and bind to protein to form an antigen. These molecules are absorbed through the skin and activate epidermal Langerhans cells, which in turn stimulate naïve T-cells to generate antigen- reactive CD8 and CD4 cells (sensitization). Further exposure to the specific antigen leads to inflammatory cellular exudates and release of toxic mediators, with clinically evident ACD.

Irritant CD involves a non-immunologic response to a mild skin irritant, such as solvents or soaps. Prolonged exposure causes disturbance of cell hydration as a result of the defatting action of irritants, with resultant xerosis of the skin.

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Clinical manifestations

CD is characterized by clearly demarcated areas of rash at sites of exposure. Acute lesions are pruritic vesicles on a background of erythema (6.3). In subacute stages, erythema and scaling are prominent, although some vesiculation may persist. Chronic lesions are characterized by dryness, lichenification, and scaling. The rash usually improves on removal of the offending agents but this is not always the case, especially if the exposure period has been long.

Appearances of different forms of CD are similar to each other and indeed may be indistinguishable from AD (Table 6.2). Other differential diagnoses include nummular eczema, seborrheic dermatitis, and psoriasiform dermatitis.

6.3 Acute ACD of the hands to latex. Although there was a positive reaction on skin prick test to latex, there was no clinical evidence of immediate reactivity to latex. The patient had a negative patch test to other rubber constituents on patch test, but had a positive challenge to rubber gloves (‘glove finger test’).

Table 6.2 Features differentiating AD and CD

AD CD

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Allergic asthma or allergic

Commonly absent rhinitis

Commonly present

Total IgE

Positive skin prick

Positive patch test

tests

Age of onset

<5 years

>5 years

Both diseases present with chronic or chronically relapsing erythematous and papulovesicular dermatitis

Management

Diagnosis

A detailed history, including occupational history, is mandatory. The appearance of CD may coincide with taking up of a new job or a new chemical process initiated at work, which may have led to exposure to a contact sensitizer (6.4). However, sometime patients present with chronic dermatitis with no clear history of exposure to a particular allergen or irritant.

CD initially involves the area of the skin that has been directly exposed but later it may spread to adjacent areas and more distant sites. The distribution of CD often provides support for the diagnosis and clues to the specific cause (Table 6.3). An erythematous scaling plaque in areas where metal jewelry is in contact with the skin is suggestive of ACD to nickel. Face and eyelids dermatitis is often due to a cosmetic allergy (6.5). Hands may be involved in ACD due to occupational exposure. ACD to plants is often characterized by linear lesions. Photoallergic dermatitis involves the more exposed areas of skin (face, hands, and feet). In contrast, textile-related allergens produce dermatitis of clothed areas. Poor response to standard treatments of AD should also suggest the possibility of ACD, as an alternative or concomitant diagnosis.

Patients should be patch tested when contact allergy is suspected. Patch testing is a procedure that is well-characterized, and the reactions are quantified with a validated scoring system (Table 6.4). The standard battery incorporates antigens that will cause most cases of ACD (70–80%). However, there are nearly 3,000 potential environmental allergens, and more extensive testing may be required. This might involve incorporation of additional chemicals into the patch testing procedure, depending on the history and the specific circumstances (6.6). Alternatively, offending agents may be tested under conditions of normal use (6.7). Interpretation of patch testing should always be done with clues obtained from the history and physical examination, as both false-positive and false-negative reactions occur. Photopatch testing may be useful when photoallergic dermatitis is suspected. In difficult cases, skin biopsy may be indicated to exclude other diagnoses, but it may not confirm CD.

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6.4 This patient developed ACD of hands and face 3 months after taking a factory job using glues to join fibreglass items. Patch test to a standard battery revealed a positive reaction to epoxy resin. He was moved to a different area of the factory which resulted in resolution of his symptoms.

6.5 ACD of the face due to cosmetics.

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Table 6.3 Causes of ACD according to the area

affected

Area affected Common causes Eyelids

Cosmetics, poison ivy Hands

Rubber products, epoxy resin, preservatives Face

Cosmetics, UV light, wool alcohol, hair dyes Neck Nickel, cosmetics Trunk Nickel, rubber Axilla

Deodorants, detergents, formaldehyde

Lower legs Neomycin, epoxy resin

Table 6.4 American Contact Dermatitis Society

patch test interpretation

Grade Characteristics +++

Coalescing vesiculobullous papules ++

Erythema, oedema, discrete vesicles +

Erythema, infiltration, discrete papules ±/? Doubtful reaction, macular erythema – No reaction IR Irritant response

6.6 This patient worked as a

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the left side) to fragrance mix (mild reaction) and p-phenylenediamine, present in hair dyes (strong reaction). In addition, she had moderate to strong reactions to the dyes she was using at work (patch test applied on the right side).

6.7 Latex glove finger test. A ‘use test’ may be helpful where there is a history of a dermal reaction on direct contact.

Treatment

Identification and removal of the offending agent is the mainstay of treatment of CD (6.8) . The history might be suggestive of an allergen, but this should be confirmed with a patch test. Once identified, the allergen or irritant should be excluded from the patient’s environment. However, this may not always be possible, especially for occupational agents. Gloves and protecting gear should be used by all workers exposed to known sensitizing agents, and may provide a solution for mild sensitizing agents for patients who are not able to change occupation. If the history does not provide a clue, patch test to

a standard battery may be helpful, but any positive result should be interpreted with caution. If a patch test is negative, the diagnosis should be reviewed. If no agent can be found, symptomatic treatment may be the only option.

Barrier creams may help with dryness, and antihistamines might provide some relief from itching. Exacerbations should be treated with high-potency, topical corticosteroids and, occasionally, a course of oral steroid may be needed. Severe ACD may require phototherapy or other anti-inflammatory agents.

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6.8 Management of CD.